Method for making a double helix type of supported fire detector sensor

ABSTRACT

A METHOD PROVIDING A DOUBLE HELIX FOR TWO LINEARLY EXTENDING MEMBERS HAVING QUITE DIFFERENT RIGIDITIES. THE MORE RIGID MEMBERS ARE TWISTED TOGETHER IN PAIRS TO DEFORM THEM INTO A DOUBLE HELIX OF THE DESIRED NUMBER OF TURNS PER LENGTH. THE TWO MEMBERS ARE THAN UNTHREADED FROM EACH OTHER WITHOUT FURTHER DEFORMING THEM, AND THE MORE FLEXIBLE MEMBER IS WOUND INTO EACH OF THE HELICALLY SHAPED MOVE RIGID MEMBERS, ONLY THE MORE FLEXIBLE MEMBER BEING DEFORMED, TO GIVE TWO OF THE REQUIRED ASSEMBLIES.

Nov. 2, 1971 M. E. TYLER METHOD FOR MAKING A DOUBLE HELIX TYPE OF SUPPORTED FIRE DETECTOR SENSOR Filed Oct. 21, 1969 OW, a/JZM M ATTORNEYS United States Patent 3,616,531 METHOD FOR MAKING A DOUBLE HELIX TYPE OF SUPPORTED FIRE DETECTOR SENSOR Maurice E. Tyler, Orinda, Calif., assignor to John E. Lindberg, Lafayette, Calif. Filed Oct. 21, 1969, Ser. No. 868,013 Int. Cl. H01c 7/04 U.S. Cl. 29--612 2 Claims ABSTRACT OF THE DISCLOSURE A method of providing a double helix for two linearly extending members having quite different rigidities. The more rigid members are twisted together in pairs to deform them into a double helix of the desired number of turns per length. The two members are then unthreaded from each other without further deforming them, and the more flexible member is wound into each of the helically shaped more rigid members, only the more flexible member being deformed, to give two of the required assemblies.

This invention relates to a method for manufacturing a fire detector or other type of sensor in which two tubes are helically wound together and in which one tube is much stronger and much less flexible than the other tube.

As shown in U.S. application Ser. No. 705,086 filed Feb. 13, 1968, an excellent fire detection system can incorporate a support member and a sensor wound together in a double helix. The support member is usually somewhat larger in diameter and is much more rigid and much stronger than the sensor member. In fact, the purpose of the support member is to strengthen the sensor, which cannot be made of such strong material by itself and still retain the desired sensitivity, as well as some other desired properties. The double-helix structure of support and sensor has proved to be very practical, the only difficulty being that it was diflicult to manufacture.

When attempts were made to manufacture the unit commercially, the obvious method of manufacture proved to be impracticalthat is simply using a lathe to wind the support tube and sensor tube directly about each other. What happened was that the more rigid support member remained linear and the sensor tube was wound around it in a single helix. The resulting structure was completely unsatisfactory, for the double helix is necessary to proper operation. Manufacture thus proceeded as a hand operation until the present invention was arrived at.

In this invention, two support members of identical characteristics are twisted together to deform them into a double helix, as by employing a lathe. Then the two support members are separated from each other without distorting their individual helix shape by unthreading one relative to the other. Then a sensor is assembled to each support member, as by hand winding. The flexibility of the sensor enables it to follow the helix of the support member perfectly, only the sensor being deformed, and thereby to make the desired double helix.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment.

In the drawings:

FIG. 1 is a view in perspective showing a lathe set up for manufacturing the double helix, before the winding.

FIG. 2 is an enlarged end elevation view of the spindle of the lathe shown in an enlargement as in FIG. 1.

FIG. 3 is an enlarged end elevation view of the special tailstock member of the lathe, a non-rotating member.

FIG. 4 is a fragmentary view in side elevation of one of the completed sensor-support assemblies.

3,616,531 Patented Nov. 2,, 1971 "ice FIG. 5 is an enlarged view in section taken along the line 55.

The invention may employ a standard lathe 10 with a rotating spindle 11. The usual tailstock 12 is not used, and a special sliding tailstock assembly 13 is used instead.

The rotating spindle 11 has a chuck 14 (FIG. 2) with two openings 15 and 16 both tangent to the center line 17 and therefore to each other, as shown in FIG. 2. Into each of these openings is inserted one of the support members 20 and 21 (see FIG. 1).

The special tailstock 13 is mounted for free sliding movement along the lathe bed 18 but no rotary movement. It may comprise two pieces 22 and 23 tightened against each other by bolts 24, and, when clamped together they provided two openings 25 and 26 tangent to each other and of the same size. Whether they are horizontal or vertical or diagonal relative to each other does not matter, except that clamping is easier when they are horizontal as shown. The reason for having the openings 15, 16 and 25, 26 in each pair tangent to each other is that it is desired to produce a double helix, each having a zero inner diameter i.e., the inner surface of each support member 20, 21 is always tangent to the center line 17.

The pair of support members 20 and 21 are secured at one end in the chuck openings 15, 16 and at the other end in the openings 25 and 26, so that they cannot rotate on their individual axes, and then the lathe 10 is started and slowly rotates the chuck 14. The number of rotations is counted and the resulting shortening in the length of the support members 20, 21 as they are twisted together is accommodated by the free sliding action of the sliding member 27 which supports the tailstock chuck 13 on the lathe bed 18. By counting the number of rotations and knowing the length of the support members 20 and 21, one can get a desired number of turns per inch. I have found it advisable to wind the two support members 20 and 21 a little bit past where I want them to be, so that when I release them, their natural elasticity brings them back to where they should be. This amount varies, of course, with the material being used, depending upon its elasticity and modulus, but is easily arrived at experimentally for any one material and after that can be used with very slight tolerances.

After the two support members 20 and 21 are wound together in the shape which eventually they are to take, I stop the lathe 10, take them out, and then separate them from each other by unwinding them relative to each other, somewhat in the manner of unthreading a screw from its Opening. When this is done, I have two separate support members 20 and 21, each helical in shape. Then I wind by hand a sensor member 30 around each support member, maintaining the member 30 in line contact with its support member 20 or 21. This is a very rapid operation, for the sensor member 30 is relatively flexible, and in a few moments the double helix shown in FIGS. 4 and 5 is completed. Part of the reason for this flexibility may be that the more rigid support member 20 may be a solid rod, whereas the sensor 30 is usually a thin-walled tube, as shown in FIG. 5.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A method of making a double helix type of supported fire detector sensor assembly from a wire-like hollow sensor tube and a more rigid wire-like support member, comprising:

(a) placing the support members in pairs,

(b) twisting together a pair of said support members to deform both of them into a double helix of a desired number of turns per length,

() unthreading those two support members apart from each other while preserving intact the helical shape of each, and

(d) winding in helically a separate sensor to each of the support members while maintaining a line contact between each sensor and its support member, deforming the sensor but not the helical support memher, to give two of the required assemblies.

2. A method of providing a double helix for two linearly extending members having quite different rigidities comprising:

(a) selecting the more rigid member in pairs,

(b) twisting together a pair of said more rigid members to deform them into a double helix of the desired number of turns per length,

(0) unthreading those two members apart from each other, while preserving intact the helical shape of each, and

4 (d) winding in helically one of the more flexible members to each of the more rigid members, deforming only the more flexible member, to give two of the required assemblies.

References Cited UNITED STATES PATENTS 2,091,245 8/1937 Thomas -149 2,2l6,758 10/1940 Schmidt 29-505 2,469,167 5/1949 Little 174-42 2,597,226 5/1952 Coates 29-610 X 3,485,101 12/1969 Lindberg et al. 73-343 FOREIGN PATENTS 687,909 6 /1964- Canada 140-149 JOHN F. CAMPBELL, Primary Examiner V. A. DIPALMA, Assistant Examiner US. Cl. X.R. 

